Cities 7 to 5 kya

7000 to 5000 years ago was the warmest time
of the inter-glacial, much warmer than now. Plants and villages grew quickly. In Iraq
and Egypt, in India and China, there were river valleys which flooded every spring and replaced
the minerals of the soil. These valleys stayed fertile for many years. Villages
here grew into cities.

The settled way of life led to an increase
in food production and population. It also let people specialize in one job,
and this led to many inventions: farming tools; clay
pottery and bricks; wheels; cast bronze tools and weapons; reading and writing.
From the earliest writing we know a little about how these cities worked.

At first, cities were led by priest-kings.
Later, when fighting with nomads and other cities became more important, the
jobs of king and priest became separated. These leaders learnt how to organize
people to build canals, city walls, temples and grain stores to carry the city
through crop failures. The kings made laws which were
written down. Astronomer-priests learnt how to use the stars to work out when
the floods would come and when to plant seeds. Others discovered mathematics
and used it to plan new buildings.